1. Field of the Invention
The present invention relates to a bubble jet-type inkjet print head chip, and more particularly, to an inkjet print head chip in which heaters are mounted to heat ink, and an ink-jet print head using same.
2. Description of the Related Art
An inkjet printer is any printer that fires extremely small droplets of ink onto media to create an image. Different types of inkjet printers form droplets of ink in different ways.
One of the most common techniques used to form droplets is the bubble jet. In a bubble jet printer, tiny heaters create heat, and this heat vaporizes ink to create a bubble in a substantially bounded volume of ink. The bubble expands and increases the pressure of the volume of ink. The pressure increase, in turn, causes droplets to form and to be ejected or fired through nozzles in the print head.
The heaters of a bubble jet printer are generally formed by a conventional semiconductor manufacturing process. On a semiconductor substrate such as a silicon wafer etc., insulation layers are formed, heaters are deposited, and patterns are formed. Then, connection electrodes are formed, and insulation layers for insulating the upper sides of the heaters and ink are deposited to complete the formation of the heaters.
The insulation layers formed under and above the heaters serve multiple functions. The lower insulation layers underneath the heaters block the loss of heat generated by the heaters through the silicon substrate, and electrically insulate the semiconductor silicon and the heaters. The upper insulation layers above the heaters electrically insulate the heaters and ink, prevent the heaters from corrosion resulting from chemical reactions with corrosive ink, and protect the heaters from damage caused by cavitation shocks occurring when ink bubbles collapse. Various substances may be used to form the upper and lower insulation layers so long as they have physical properties satisfying the above requirements. Further, the substances for the upper and lower insulation layers can be manufactured into the layers through a semiconductor manufacturing process, and have excellent junction properties between layers.
FIG. 1 illustrates a structure of a conventional inkjet print head chip constructed in consideration of the above requirements and conditions.
In FIG. 1, NPN transistors, which drive heaters, are formed on a substrate through a conventional semiconductor manufacturing process. In one NPN transistor, the collector regions 2, 4, 7, and 11 completely surround the emitter region 10 and the base regions 5 and 8. Further, an insulation layer 13 of SiO2 film is formed over the NPN transistor through a thermal oxidation process, over which a thermal accumulation layer 14 of silicon oxide film is deposited. Thereafter, a heater 15 and an electrode layer 16 are formed in order before a protection layer 17 is formed. A nozzle plate 19 having ink nozzle holes is provided to cover the top of the print head chip. The thermal accumulation layer 14 functions as a lower or underneath insulation layer insulating the electrodes 12 of the transistor and the electrodes 16 of the heater 15. The protection layer 17 functions as an upper or over insulation layer insulating the electrodes of the heater from one another.
The lower insulation layer underneath the heater cuts off heat radiated when the ink is heated by the heater to maximize the supply of the heater heat to ink, and, thereafter, externally radiates the heat remaining in the heater after firing or ejecting ink before returning to its initial state. Therefore, the lower insulation layer carries out the contradictory functions of insulating the lower side or underside when the heater is heating ink and externally radiating any remaining heat from the heater after heating.
While the lower insulation layer of SiO2 used as a heat accumulation layer has excellent radiation properties, it has limited heat insulating characteristics. Therefore, to achieve acceptable insulation performance, it is necessary to increase the thickness of the insulation layer. However, increasing the thickness also decreases the cooling time. A shortened cooling time makes it difficult to enhance the operation frequency of the heater, that is, the firing or ejecting frequency of the inkjet print head.
Further, in case of the bubble jet-type inkjet print heads, ink viscosity increases as the ambient temperature of ink is lowered, which occasionally causes ink not to be fired or ejected. In winter, for example, as the temperature of an office reaches about 15° C., the ink viscosity increases to a level that printing is not performed on the first one or two sheets of paper at the start of a print job.
In order to solve this problem, it is necessary to pre-heat ink to a certain temperature when the ambient temperature of ink is lowered. To accomplish this pre-heating of the ink, a conventional inkjet print head is provided with an extra heater. When activated, the extra heater heats the entire head chip to which the heater is mounted to over 30° C. However, such a method heats the entire inkjet print head chip to pre-heat ink over a certain temperature, which causes the consumption of much energy for the heating and the transistors in the inkjet print head chip may have malfunctions due to the heat.